The present invention relates to methods and systems for thermal forming an object. More specifically, the present invention relates to methods and systems for selectively heating a material to be disposed over or into a mold.
Various techniques for thermal forming objects are currently used in the art. These include thin-gauge thermal forming techniques, where thin sheets or films (usually having a thickness of less than 0.6 inches) of plastic are used to form relatively portable objects such as dishware, food packaging products, plastic blisters for packaging of pharmaceutical products, and the like. These also include thick-gauge thermal forming techniques, where thicker sheets (usually having a thickness greater than 1.2 inches) of plastic are used to form relatively bulky objects, such as cosmetic surfaces on automobiles, medical equipment, kitchen appliances, and the like.
In many techniques, the sheeted plastic material is first heated, and then formed into the shape of the desired object using a mold. Heating is typically done with a single unit including one or more heating coils. Numerous problems arise with uneven distributions of heat in many existing systems. In the case of a single heating coil, portions of the plastic located under the heating coil are heated to a much greater extent than portions of the plastic located away from the heating coil. In the case of multiple heating coils, portions of plastic located under the heating coils are heated to a greater extent than portions of the plastic located between heating coils.
Uneven heat distributions cause various problems in the thermal forming process. For example, the malleability of the heated plastic varies, resulting in inaccurate forming over a mold. For another example, portions of the heated plastic may be heated too much so as to provide a desired average heat and thus malleability to form the plastic over the mold, where the overheating causes deformations, weaknesses, etc. in the plastic composition. In applications which require high precision molds, such as in the formation of dental appliances that must accurately conform to a mold within a tolerance of mere micrometers, these problems create significant burdens and inefficiencies in the thermal forming process, and potentially deficiencies in product effectiveness.
Further, existing techniques do not take into consideration changes or differences in plastic and/or molds. That is, the same heating coils and amount of heat is produced even if the plastic sheets (or molds) provided at the input are changed (to be thicker or thinner) for forming different objects. In this case, suboptimal heating is performed on the subsequent sheets, resulting again in inefficiencies and product expansion limitations.
Accordingly, it is desirable to overcome such deficiencies so as to improve the quality of objects that are formed by thermal forming, increase the efficiency of manufacturing objects via thermal forming, reduce the amount of waste generated by current thermal forming systems and processes, and increase the number of applications for which a single thermal forming system may be used.